From the US EPA
You can’t see, smell or taste radon, but it could be present at a dangerous level in your home. Radon is the leading cause of lung cancer deaths among nonsmokers in America and claims the lives of about 21,000 Americans each year. In fact, the EPA and the U.S. Surgeon General urge all Americans to protect their health by testing their homes, schools and other buildings for radon.
Exposure to radon is a preventable health risk and testing radon levels in your home can help prevent unnecessary exposure. If a high radon level is detected in your home, you can take steps to fix the problem to protect yourself and your family.